Chunky yarn?

I've agreed to knit a scarf for a friend, and while it's a very basic pattern (he's studying Maths at university, and is geeky enough to want a mobius scarf, which is the kind of thing you can made quite easily on a big circular needle), I can't quite find the right type of yarn. I'd like to make it from something relatively chunky so that I can knit it up in a couple of evenings, but it looks like almost everything designed for needles 4mm and larger contains at least some wool. It just seems to be difficult to find a good, thick, vegan yarn.

Since I'm based in Scotland and don't want to pay horrific shipping costs, I'm looking for something which can be bought within the UK (bonus points if John Lewis stock it, as there's one that I pass on the way home from work), and obviously it shouldn't be something too fluffy and girly because he just wouldn't wear something made from some of the weirder novelty yarns.